The ECM is located in the front of the center console on the transmission hump. The wiring is easily reached by removing the small black panel just to the front of the center console on the passenger side. the wire is in the middle row, 7th one in from the left.

I dont know if you'll get much out of it.. the tach wire is just a wire that sends pulses of DC current to the injectors.. i'm not sure if it changes when it goes through the firewall and connects to the ecm.. just my 2 cents.

The ECM is located in the front of the center console on the transmission hump. The wiring is easily reached by removing the small black panel just to the front of the center console on the passenger side. the wire is in the middle row, 7th one in from the left.

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There are about 3 black panels, all the center of my maxima, and I dont recall any on the passenger side.

Am I looking in the hump (floor) or the one facing forward - the dashboard?

I think you'll have problems with reading it from there with a PIC or other mcu. It's very noisy, electrically.

You are right. That particular car is coil on plug though, so there are 6 coils. So my first response was incorrect. I posted a pic of the wiring diagram for that vehicle and the wire mentioned above is correct. It will be a very "clean" signal because it is produced by a control module for the express purpose of running the tachometer.